Lubricating oil composition



United States Patent 3,249,544 LUBRICATING OIL COMPOSITION Elaine M. Hofiman, New Brunswick, and Harold Shaub,

Elizabeth, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Mar. 14, 1963, Ser. No. 265,065 7 Qlaims. (Cl. 252-515) This invention relates to lubricating oil compositions containing a synergistic mixture of a partial ester of a polycarboxylic aromatic acid and N,N'-disalicylidene- 1,2-propanediamine or N,N'-disalicylidene-1,2-ethanediamine, which synergistic mixture is useful in lubricating oil compositions to inhibit corrosion of magnesium.

The use of various ester oil compositions for lubrication of modern day aircraft engines is well known. However, many of these ester oil compositions are corrosive to the magnesium parts of the constant speed drive unit used in conjunction with turbo-fan engines. These constant speed drive units are lubricated with the same oil composition used for lubrication of the turbo-fan engines, and corrosion of magnesium parts of said drive units occurs with the normal type of synthetic ester aircraft engine lubricating oil composition. It has now been found that this magnesium corrosion can be substantially inhibited by the incorporation of a synergistic mixture of various esters of polycarboxylic aromatic esters in conjunction with certain amines which are known as metal deactivators. While inhibiting magnesium corrosion, this synergistic composition does not appear to affect adversely any of the other desirable properties of the ester oil compositions.

The partial esters of the aromatic acid include those having the general formula:

wherein R represents an aromatic nucleus having 6 carbon atoms in the ring; R is an alkyl radical containing 1 to 20, e.g. to 13, carbon atoms; n is a number of 1 to 3; while In is a number of l to 3, such that m+n=3 if the aromatic acid is tribasic, or m+n=4 if the aromatic acid is tetrabasic. Partial esters of this type and methods for their preparation are described in US. Patent 3,019,188.

The aromatic polycarboxylic acids used in preparing the above type of esters include the following:

0 O OH (I) O OH(trimesie) C 0 OH(trime11itic) HO O C C O OH HO O C O O OH (I? O OH O O OH(prehnitic) HO O C C O OH Where they exist, the corresponding partial or full acid anhydrides may also be used; e.g. pyromellitic acid anhydride which has the structure:

10 f fi 0 o The 'amine component includes those having the general formula:

OH HO- H R H where R is hydrogen or a methyl group. When R is hydrogen, the amine is N,N'-disalicylidene-l,Z-ethanediamine. When R is methyl the amine is N,N'-disalicylidene-LZ-propanediamine. The latter material is commercially available from the Dupont Co. as Metal Deactivator.

About 0.1 to 2.0%, preferably 0.18 to 1.0%, of the amine and about 0.1 to 2%, preferably 0.18 to 0.5%, of the partial ester of the aromatic polycarboxylic acid will generally be used in a lubricating composition. The total amount of both these materials that will be used will be about 0.2 to 4.0%, preferably 0.36 to 2.0%. All of said weight percents being based upon the total weight of the lubricating composition. The synergistic combination of the two materials is generally applicable to lubricating oils, and in particular applicable to synthetic ester type lubricating oils.

The synthetic ester oils include diesters represented by the formula:

wherein R is a straight or branched chain hydrocarbon radical of a C to C alkanedioic acid, R represents an alkyl radical of a C to C branched or straight chain allcanol and the total number of carbon atoms in the molecule is about 20 or more. Specific examples of such diesters include di-Z-ethylhexyl sebacate, di-C Oxo-adipate, di-C Oxo adipate, etc. Recently, fully esterified esters prepared from alcohols having no fl-hydrogen and carboxylic acids having no a-hydrogen have become known for aviation use. These esters are particularly good for high temperature lubrication since they are exceptionally stable because they are completely hindered at the ester linkage, which generally is otherwise the weakest link in an ester molecule from the standpoint of heat stability, oxidation and hydrolysis. The saturated alcohol used to prepare these high temperature esters will generally have 1 to 4 hydroxy groups, and will be 50 free of hydrogen atoms attached to the carbon atoms beta to each of said hydroxy groups, i.e. the alcohol is a neo alcohol. The alcohol will generally have a total of 4 to 10 carbon atoms. The acid used to prepare the high temperature esters is usually saturated, preferably has 65 one or two carboxylic acid groups and will be free of hydrogen atoms attached to the carbon atoms alpha to the carboxylic acid group or groups. The carboxylic acid will usually contain 7 to 20 carbon atoms. Conventional esterification procedures can be used to form the high temperature esters.

More specifically, the alcohol used to form the aforesaid high temperature esters will include those represented by the general formula:

5 H(|JX RCCHOH H-(f-X H where R is a C to C alkyl group, or a CH OH group, and X is either H or OH. Examples of such alcohols include trimethylolethane, trimethylolpropane, and alcohols having the structures:

(llHg (3H3 CHaCHC H2CCH2OH (3H3 CH;-CHzOH2(lJCHzOH;and C(CHrOHM Also, included among the no fi-hydrogen or neo alcohols are cyclic alcohols such as the dihydric alcohol having the formula:

C 3 CH3 HOHC C H-OH The no a-hydrogen acid will include those represented by the general formula:

in the case of dicarboxylic acids, R" is preferably an alkyl group such as methyl or ethyl. Examples of such acids are a,a-climethyl valeric; ot-ethyl, u-methyl caproic;

oc,a-dimethyl propionic; a,a-dimethyl octanoic; a,a,zx, x-

tetramethyl pimelic; etc.

The synergistic additive combination of the invention can also be used in compositions containing complex esters which are frequently used as blending agents with other less viscous esters to tailor-make an ester lubricant composition. The more important of the complex esters can be represented by the general formula:

wherein R and R are alkyl radicals of monohydric alcohol, preferably having no beta hydrogen, R and R are hydrocarbon radicals of dicarboxylic acid, and R is the divalent hydrocarbon radical of a glycol or polyglycol, which glycol or polyglycol preferably is a neo glycol or polyglycol, i.e. having no beta hydrogen. n

-in the complex ester molecule will range from 1 to 6,

usually 1 to 3, depending upon the product viscosity desired which is controlled by the relative molar ratio of the glycol or polyglycol to the dicarboxylic acid. In preparing the complex ester, there will usually be some simple diester formed, i.e. n=0, but this will generally be a minor portion, eg 10 to 40 wt. percent of the complex ester esterification reaction product. Processes for forming complex esters are well known in the art, eg see US. Patents 2,575,196 and 2,956,954.

Some specific materials used in preparing the above types of complex esters are as follows: neo alcohols having 6 to 13 carbon atoms such as 2,2,4-trimethylpentanoll; 2,2-dimethylhexanol-1; 2,2-dimethylpentanol-l; l-methylcyclohexylmethanol; 2,2-dimethylbutanol-1; 2,2-dimethyldecanol-l; C to C dicarboxylic acids such as sebacic, adipic, azelaic and dodecanedioic acid; neo glycols such as 2,2-dimethylpr0panediol-1,3; 2-ethyl-2-butyl propanediol-l,3; 2,2-diethylpropanediol-1,3; 2,2-dimethylbutanediol-l,3; etc.

In general the complex esters will have a total of 20 to 80, preferably 40 to 65, carbon atoms per molecule. Preferably the complex esters are prepared by reacting 1 mole of glycol, 2 moles of dicarboxylic acid and 2 moles of alcohol. This will result in about 35 wt. percent of diester of the dicarboxylic acid and alcohol, and about wt. percent of complex ester of the formula: Alcohol- Acid-(Glycol-Acid) -Alcohol, where x averages about 1.8.

Various other additives can also be added to the lubricating compositions of the invention in amounts of about 0.001 to 10.0 weight percent each, based on the total weight of the composition. Examples of such additives include: rust preventives such as calcium petroleum sulfonate or sorbitan monooleate; V.I. improvers such as the polymethacrylates; oxidation inhibitors such as phenylalpha-naphthylamine, para-aminodiphenylamine, 3,7-dioctyl phenothiazine, p,p-dioctyldiphenylamine and phenothiazine; load carrying agents such as tricresyl phosphate and free sebacic acid; pour point depressants; polymeric detergents; dyes; V.I. improvers; grease thickeners; other ester oils; other synthetic lubricating oils; and the like.

A particularly desirable type of additive, especially when relatively large amounts of nitrogen containing aromatic types of antioxidants are used which tend to form sludge during high temperature use, are the dispersant V1, improvers. These polymeric materials generally have viscosities at 210 F. of 300 to 700 cs., preferably 600 to 700 cs., as 30% to 50% concentrates in di-Z-ethylhexyl sebacate. These polymers consist of a carbon to carbon backbone having various side chains which impart'to the polymer its viscosity index and dispersancy improving properties. One type of such polymers is that prepared by copolymerizing a polar monomer with various unsaturated ester. The esters can be esters of unsaturated monoor dicarboxylic acid, or esters of unsaturated monohydric alcohols, as well as various combinations thereof.

The polar monomers include 2-N-vinyl pyrrolidone, maleic anhydride, alkenes, ether substituted alkenes and hydroxy substituted alkenes.

The preferred ester monomers are prepared from C to C carboxylic acids and C to C alcohols with at least one of said acid or said alcohol containing an ethylenic unsaturation. Usually about 1 to 20 mol. percent of the polymer will be the polar monomer, while the remainder is the ester monomer. The copolymerization is generally carried out by using peroxide type catalysts such as benzoyl peroxide under conventional conditions.

A specific copolymer which was used in several of the examples of the invention is commercially available under the name Acryloid HF 866. This material is a concentrate of about 30 wt. percent copolymer of a methacrylate ester and 2-N-vinyl pyrrolidone in about wt. percent di-2-ethylhexyl sebacate. Said concentrate had a viscosity of about 600 cs., at 210 F., while the intrinsic viscosity of the copolymer in toluene was about .88. The aforesaid methacrylate ester component of the copolymer comprises a mixture of esters having alkyl groups within the range of about 4 to 16 carbon atoms and averaging about 9 carbon atoms per alkyl group in the ester.

The invention Will be further understood by reference to the following examples which include a preferred embodiment of the invention.

EXAMPLE I The synergistic additive combination of the invention was tested in a fully compounded aircraft engine lubricating oil composition to demonstrate its magnesium oxidation inhibiting activity. The base oil of said composition consisted of 85 wt. percent of di-2,2-44tri.methylpentyl 'sebacate and 15 wt. percent of a complex ester composition. The complex ester composition was prepared by the simultaneous reaction of 2 molar propor tions of 2,2,4-trimethylpentanol-1, 2 molar proportions of sebacic acid, and 1 molar proportion of neopentyl glycol. To 100 parts by weight of this base oil was added 3 parts by weight of phenyl-alpha-naphthylamine, 2 parts by weight of A-cryloid HF-866, and 2 parts by weight of p,p-dioctyldiphenylamine.

Into the previously described synthetic lubricant was dissolved by simple mixing varying amounts of N,N- disalicylidene-l,2-propanediamine, and of the monoester of trimellitic acid and C Oxo alcohol, as Well as a combination of these two materials.

The C Oxo alcohol used in preparing the monoester was obtained by subjecting a C C monoolefin feed to the 0x0 process which involves converting the feed to a C7 aldehyde by reaction with carbon monoxide and hydrogen using a cobalt carbonyl catalyst, which aldehyde is then hydrogenated to the alcohol which is recovered by distillation. The resulting C Oxo alcohol is an isomeric mixture of branched chain (mainly methyl branched) aliphatic primary alcohols. The Oxo alcohols are well known in the art, e.g. see U.S. Patent 3,019,188.

The resulting compositions were subjected to tests for corrosivity to magnesium, copper, iron, aluminum, silver and titanium according to Oxidation Corrosion Stability (O.C.S.) test described in Military Specification MIL-L- 7808C, With the exception that the test was run at a temperature of 450 F. in place of the 347 F. standard test temperature. This was done in order to accelerate the test. Briefly described, this test involves suspending Weighed strips of the metals to be tested in the oil sample maintained at 450 F. for 48 hours, while air is bubbled through the sample. The weighed metal strips are reweighed after the test period and the weight change is thereby determined and reported in terms of milligrams per square cm. of metal surface. A Weight loss is reported as minus while a Weight gained is reported as plus As demonstrated by Table I, while neither the amine nor the partial ester per se were effective in decreasing magnesium corrosion, yet the combination of these two materials drastically reduced the level of magnesium corrosion. At the same time, no detrimental effects were obtained by use of the combination with regard to corrosion of the other metals under test.

EXAMPLE II A second series of compositions were made 'up by adding varying amounts of N,N-disalicylidene-l,2-propanediamine and mono-C Oxo trimellitate to the same fully compounded aircraft engine lubricating oil composition of Example I. The resulting compositions were then subjected to the Oxidation Corrosion Stability Test at 450 F., previously described. The amount of additive used and the results obtained are summarized in Table II which tfOllOWSZ Table II Additive:

Mon0CB Oxo trimellitate, percent- 1 0. 18 0. 25 N ,N-disalicylidene- 1,2-propanediamine, percent 1 O. 35 0. 18 0. 25

As seen by Table II, the presence of 0.18 Wt. percent of N,N-disa-licylidene-1,2-propanediamine and 0.18 Wt. percent of mono-C OX0 trimellitate resulted in a magnesium corrosion of only 0.04 milligrams per square centimeter of test surface, while 1 wt. percent of the N,N'-disalicylidene-1,2-propanediamine alone gave 0.13 mg/cf? of magnesium corrosion and 1% of the partial ester alone gave 17.47 mg./cm. of magnesium corrosion. This data therefore clearly illustrates the synergistic and unexpected reduction in magnesium corrosion obtained by using the combination of the two additive materials of the invention, as opposed to using larger quantities of either additive material alone.

EXAMPLE III To :further demonstrate the synergistic eifect of the inventive combination, a third series of tests were run on the fully compounded aircraft engine lubricating oil composition of Example I containing in addition varying amounts of the mono-C Oxo trimellitate and of the N,N- disa licylidene-1,2-propanediamine. These tests were run according to the 450 F. Oxidation Corrosion Stability test previously described and the results obtained are summarized in Table HI which follows:

Table III Additive:

Mono-gs 0x0 trmellitate, percent. 0. 0 1. 0 0.0 0. 5 0.35 0. 0 0. 18 0. 5 0. 0 0. 25 N N isalic li med 2- ro aneiliamine, p ercentniu in 0.0 0.0 1.0 0.5 0.0 0.35 0.18 0.0 0.5 0. 25 Mg. Corrosion (mg./sq.cm.) -45.08 17. 47 0. 13 0.03 26.33 --0. 25 -0.04 -14. 15 1.93 0.09

The results obtained are summarized in Table I which follows:

The above table clearly demonstrates the synergy resulting from the combination of the two additive materials with regard to inhibiting magnesium corrosion. Thus, the lubricating oil composition without either additive material gave 45.08 mg./cm. weight loss. The addition of 1 wt. percent of the mono-C Oxo trimellitate reduced the corrosion .to 17.45 mg./cm. weight loss, while 1% of the amine reduced corrosion to .13 rng./cm. weight loss. However, the use of 0.5 wt. percent of each additive reduced the corrosion to only 0.03 mg./cm. Similar results were obtained at other levels of concentration.

While the preceding examples have illustrated the additive combination of the invention in a fully formulated oil, the additive combination of the invention can also be used in ester oil alone. For example, a synthetic ester lubricating oil composition is prepared by simple mixing of 99 wt. percent di-Z-ethylhexyl sebacate, 0.5 wt. percent of N,N-disalicylidene-'1,Z-ethanediamine and 0.5 wt. percent of di-n-heptyl pyromellitate.

What is claimed is:

1. A lubricating oil composition comprising a major amount of fully esterified carboxylic acid ester lubricating oil having a tendency to corrode magnesium at elevated temperatures and a magnesium-corrosion inhibiting synergistic combination of 0.10 to 2 wt. percent of an amine selected from the \group consisting of N,N'-disalicylidene- 1,2-propanediamine and N,N'-disalicylidene-1,2-ethanediamine and about 0.1 to 2.0 wt. percent of partial ester of C to C alcohol and an aromatic carboxylic acid having 3 to 4 carboxy groups, said Wt. percent being based upon the total Weight of said composition.

2. A lubricating oil composition according to claim 1, wherein said partial ester is a monoester of C to C alcohol and said aromatic carboxylic acid has 3 carboxy groups.

3. A lubricating oil composition according to claim 1, wherein said amine is N,N-disalicylidene-1,2-propanediamine.

4. A lubricating oil composition according to claim 1, wherein said amine is N, N-disalicylidene-1,2-ethanediamine.

5. A lubricating oil composition according to claim 1, wherein said partial ester is a monoester of a C branched chain alcohol and trimellitic acid.

6. An aircraft lubricating oil composition comprising a major amount of a diester of C to C saturated aliphatic dicarboxylic acid and a C to C aliphatic saturated neo alcohol, about 0.10 to 2.0 wt. percent of an amine selected from the group consisting of N,N-disalicylidene- 1,2-propanediamine and N,N-disalicylidene-1,2-ethanediamine and about 0.10 to 2.0 wt. percent of the monoester of trimellitic acid and C branched chain saturated alcohol, and wherein said amine and said monoester are used in substantially equal amounts by Weight.

7. An aircraft lubricating oil composition according to claim 6, wherein said diester is di-2,2,4-trimethylpentyl sebacate and said amine is N,N'-disalicylidene-1,21propanediamine.

References Cited by the Examiner UNITED STATES PATENTS 2,181,122 11/1939 Downing et al. 252403 X 2,789,912 4/1957 Gleim 99163 2,813,080 11/11957 Bartlett 252403 2,894,979 7/1959 Leach 2'5256 X 2,939,842 6/1960 Thompson 2525'1.5 X 3,003,955 10/1961 Jones 252392 X 3,019,188 1/1962 Craven et al 252-57 3,071,451 1/1963 Schmerling 25251.5 X

DANIEL E. WYMAN, Primary Examiner.

JOSEPH R. LIBERMAN, Examiner. 

1. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF FULLY ESTERIFIED CARBOXYLIC ACID ESTER LUBRICATING OIL HAVING A TENDENCY TO CORRODE MAGNESIUM AT ELEVATED TEMPERATURES AND A MAGNESIUM-CORROSION INHIBITING SYNERGISTIC COMBINATION OF 0.10 TO 2 WT. PERCENT OF AN AMINE SELECTED FROM THE GROUP CONSISTING OF N,N''-DISALICYLIDENE1,2-PROPANEDIAMINE AND N,N''-DISALICYLIDENE-1,2-ETHANEDIAMINE AND ABOUT 0.1 TO 2.0 WT. PERCENT OF PARTIAL ESTER OF C1 TO C20 ALCOHOL AND AN AROMATIC CARBOXYLIC ACID HAVING 3 TO 4 CARBOXY GROUPS, SAID WT. PERCENT BEING BASED UPON THE TOTAL WEIGHT OF SAID COMPOSITION. 